In cold conditions the viscosity of liquids such as engine coolant increases, in such conditions it may be necessary to increase the temperature of an internal combustion engine, for example of a vehicle, prior to starting the engine in order to efficiently start the engine, and/or it may be desirable to preheat the passenger cabin of a vehicle. Preheating the passenger cabin can be achieved using the Healing Ventilating and Air-Conditioning system (HEVAC); preheating the engine can be achieved by heating the engine coolant, normally used to cool the engine, and pumping this ‘warmed’ or ‘heated’ coolant through a fluidic circuit in the coolant system of the vehicle such that heat is transferred to the engine components. A fuel operated heater may be provided to heat the coolant; fuel normally used to power the combustion engine of the vehicle is ignited to produce heat which is transferred to the coolant. Typically an auxiliary coolant pump is used to pump the coolant about the fluidic circuit of the engine and the HEVAC when the vehicle's engine is not running; such auxiliary coolant pumps are typically less powerful than the normal coolant pump, used when the engine is running. This is due to the limited power reserves available when the engine is off, for example only power from the vehicle's battery may be available.
In extreme cold conditions, for example below −30° C., the increase in viscosity of the coolant can reduce the flow rate of the coolant when pumping the coolant about the fluidic circuit with the auxiliary coolant pump. The flow rate can be reduced to a point at which the system is unable to dissipate the heat generated by the fuel operated heater, this can lead to localised ‘boiling’ or overheating of the coolant in the region of heat transfer. Such overheating can be defected and may lead to generation of a fault code and/or render the fuel operated heater and/or vehicle inoperative, either to prevent damage to the heat exchanger or the pump or as a consequence of damage caused. Such problems can become exacerbated as the coolant temperature approaches or exceeds around −40° C.
It is therefore an aim of the present invention to overcome or at least mitigate the aforementioned problem. Other aims and advantages will become apparent form the following description and drawings.
The present invention seeks to provide an improvement in the field of fuel operated heaters which have particular application in vehicles. The invention may be utilised in applications other than for vehicles, for example it is foreseen that the invention may have application in generators, in particular portable generators, or other applications requiring an internal combustion engine.